1. Technical Field
The present invention relates to a semiconductor element using droplet discharging as typified by ink jetting, and a method for manufacturing the same. More particularly, the present invention relates to a semiconductor element that is used for a light-emitting device as typified by an electroluminescent display device, and a method for manufacturing the same.
2. Background Art
In manufacturing a semiconductor element, it has been considered the possibilities of using a droplet discharge device for forming a pattern of a thin film or a wiring, each of which is used for a semiconductor element, to reduce costs for equipment and to simplify a manufacturing process.
In this instance, various wirings such as a gate electrode, a scanning line, a signal line, and a pixel electrode for forming a semiconductor element are formed according to the procedure, that is, a composite formed by dissolving or dispersing a conductive material into a solvent is discharged from a nozzle of a droplet discharge device above a substrate or a film so that such the various wirings are formed by being directly drawn. (See Japanese Unexamined Patent Publication No. 2003-126760).
To manufacture a semiconductor element such as a thin film transistor (TFT) that is used for a light-emitting device as typified by an active matrix electroluminescent display device, it has been required to establish a structure and a process that are most appropriate to droplet discharging and that are different from a TFT manufactured by conducting repeatedly a film formation process, a patterning process, and an etching process. It has been required to simplify the structure and the process of a semiconductor element manufactured by droplet discharging with the increase in the size of a TFT substrate, for example, a substrate of more than 1×1 m or twice or three times as large as that.
Especially in case that a light-emitting element composed of layers containing organic compounds or inorganic compounds (typically, a light-emitting element utilizing electroluminescence) is driven by a TFT, a structure having at least two transistors installed with a drive TFT is required to prevent irregularities of ON current of a switching TFT provided to a pixel region. Accordingly, the simplification of a structure and a process for manufacturing a semiconductor element becomes an urgent task as a large substrate is frequently used.
The foregoing light-emitting element is composed of laminated light-emitting layers containing an organic compound or an inorganic compound, each of which has a different carrier transporting property, interposed between a pair of electrodes. Holes are injected from the electrode and electrons are injected from another electrode. The light-emitting element utilizes the phenomenon that holes injected from the electrode and electrons injected from another electrode are recombined with each other to excite an emission center, and excited molecules radiate energy as light while returning to the ground state. FIG. 1B shows a circuit structure of a pixel in the case that a light-emitting element is formed by stacking layers sequentially. When a light-emitting element is formed by stacking layers sequentially, a pixel electrode of a drive TFT 1602 serves as a hole injecting electrode (anode).
Reference numeral 1601 in FIG. 1B denotes a switching TFT for controlling ON/OFF of current flowing in a pixel. As illustrated in FIG. 1B, a drain wiring (or a source wiring) of a switching TFT 1601 is connected to a gate electrode layer of the drive TFT 1602. Since a gate insulating film or a semiconductor layer are presented between the gate electrode layer, and the source or the drain wiring (hereinafter, referred to as gate-drain), a gate electrode layer 1609 of the drive TFT 1602 is required to connect to a drain wiring 1608 of a switching TFT 1601 via an opening portion 1610 such as a contact hole (FIG. 1A). Accordingly, there has been a problem of a complicated process and a decrease in throughput and yields. Further, in case that a light-emitting element is formed by stacking layers inversely (in case that a pixel electrode of the drive TFT 1602 serves as an electron injecting electrode (cathode)) (FIG. 2), similar problem has been arisen.
In order to solve the foregoing problem, it is an object of the present invention to provide a structure of a semiconductor element, which is used for a light-emitting device, and which has proper conditions to be actively formed by droplet discharging; and a simplified method for manufacturing the semiconductor element. According to the present invention, the high throughput manufacture of a high stable semiconductor element over various sized substrates can be realized in high yields for reduced tact time can be realized.
The followings are aspects of the present invention to solve the foregoing problems.
One configuration of the present invention provides a light-emitting device, which comprises: per pixel of the light-emitting device, at least a semiconductor element for switching and a semiconductor element for driving; wherein the semiconductor element for switching and the semiconductor element for driving element, which comprises: a layer containing titanium or a titanium oxide formed over a substrate; a gate electrode layer formed over the layer; a gate insulating film formed over the gate electrode layer; a semiconductor film formed over the gate insulating film; a source electrode and a drain electrode formed over the semiconductor film; and an insulating film formed above a portion serving as a channel region in the semiconductor film; wherein the source electrode or the drain electrode of the semiconductor element for switching is connected to the gate electrode layer of the semiconductor element for driving.
According to one aspect of the present invention, at least a portion provided with a gate electrode layer in a substrate is pretreated before forming a gate electrode layer over the substrate. As the pretreatment, the formation of a layer containing titanium, titanium oxide, or the like; the formation of a film formed by polyimide, acrylic, or a material which has a skeleton formed by the bond of silicon (Si) and oxygen (O), and which includes at least hydrogen as a substituent, or at least one selected from the group consisting of fluoride, alkyl group, and aromatic hydrocarbon as the substituent; plasma treatment; or the like can be nominated. The plasma treatment is preferably conduced in atmospheric pressure.
Another configuration of the present invention provides the insulating film is preferably formed to have a thickness of 100 nm or more, more preferably, 200 nm or more, to serve as a channel protecting film. Further, the insulating film may be formed to have a laminated-layer structure. For example, a bottom layer may be formed by a film that can be formed by CVD or sputtering such as a silicon nitride film, and a top layer may be formed by a film that can be formed by droplet discharging, for example, polyimide, acrylic, or heat resistant resin such as siloxane. Alternatively, both layers may be formed by films that can be formed by droplet discharging. The semiconductor film provided with the insulating film is preferably formed to have a thinner thickness than that of another semiconductor film. Further, to obtain enough large channel mobility, the semiconductor film provided with the insulating film is preferably formed to have a thickness of 5 nm or more, preferably, 10 nm or more, more preferably, 50 nm or more.
More another configuration of the present invention provides a column-like conductor (also referred to as a pillar, plug, or the like) that is preliminarily formed over a gate electrode layer of a drive TFT that is required to be provided with a contact hole.
Still more another configuration of the present invention provides a method for manufacturing a light-emitting device having, per pixel of the light-emitting device, at least a semiconductor element for switching and a semiconductor element for driving, which comprises the steps of: for forming the semiconductor element for switching and the semiconductor element for driving, forming a gate electrode layer by discharging a composite containing a first conductive material over a substrate; forming a gate insulating film over the gate electrode layer; forming a semiconductor film over the gate insulating film; forming a semiconductor film containing an impurity element having a conductivity type over the semiconductor film; forming a source electrode and a drain electrode by discharging a composite containing a second conductive material over the semiconductor film containing an impurity element having a conductivity type; forming a source region and a drain region by removing a part of the semiconductor film containing an impurity element having a conductivity type using the source electrode and the drain electrode as a mask; forming an insulating film above a portion serving as a channel region in the semiconductor film; forming an island-like semiconductor film by removing a part of the semiconductor film using the source electrode, the drain electrode, and the insulating film as a mask; wherein a contact hole is formed by removing at least a part of the gate insulating film over the gate electrode layer of the semiconductor film for driving; and a wiring for connecting the source electrode or the drain electrode to the gate electrode layer of another semiconductor film by discharging a composite containing a third conductive material via the contact hole.
That is, the gate electrode layer is formed by droplet discharging over the substrate; the gate insulating film, the semiconductor film, the semiconductor film containing an impurity element of a single conductivity type (hereinafter, single conductivity semiconductor film) are stacked by a thin film formation method such as CVD or sputtering; and a source electrode and a drain electrode are formed by droplet discharging. Then, the source region and the drain region are formed by removing the exposed single conductivity semiconductor film by etching or the like using the source electrode and the drain electrode as a mask. And then, an insulating film capable of being formed by droplet discharging or the like is formed thereover to cover to prevent the portion serving as a channel region of the semiconductor film from removing. In addition, the insulating film serves as a channel protecting film. An island-like semiconductor film is formed by removing the exposed semiconductor film by etching or the like using the source electrode, the drain electrode, and the insulating film as masks. Through the foregoing process, a semiconductor element that seems like a channel protective type apparently can be obtained. Moreover, a desired liquid crystal display device or a light-emitting device can be obtained by providing a light-emitting element using a liquid crystal element, organic electroluminescent element, or the like, and connecting a pixel electrode to the source electrode or the drain electrode.
According to another aspect of the present invention, at least a portion provided with a gate electrode layer in a substrate is pretreated before discharging a composite containing a first conductive material over the substrate. As the pretreatment, the formation of a layer containing titanium, titanium oxide, or the like; the formation of a film formed by polyimide, acrylic, or a material which has a skeleton formed by the bond of silicon (Si) and oxygen (O), and which includes at least hydrogen as a substituent, or at least one selected from the group consisting of fluoride, alkyl group, and aromatic hydrocarbon as the substituent; plasma treatment; or the like can be nominated. The plasma treatment is preferably conduced in atmospheric pressure.
According to more another aspect of the present invention, a source region and a drain region are formed; a first insulating film is formed over the source electrode and the drain electrode by CVD or sputtering; a second insulating film is formed over the first insulating film and above the portion serving as a channel region in the semiconductor film; and an insulating film serving as a channel protective film is formed to have a two-layered structure. The second insulating film serves as not only a channel protective film but also a mask for removing a first protective film formed all over a substrate by CVD or the like. As the first insulating film, an insulating film containing silicon, preferably, a silicon nitride film is used. As the second insulating film, any insulating film can be used as long as it can be selectively formed by droplet discharging. Preferably, a film formed by polyimide; acrylic; or a substance which has a skeleton formed by the bond of silicon (Si) and oxygen (O), and which includes at least hydrogen as a substituent, or at least one selected from the group consisting of fluoride, alkyl group, and aromatic hydrocarbon as the substituent can used as the second insulating film. The insulating film is not limited to a two-layered structure; the film can be formed to have a three or more-layered structure.
A substance, which has a skeleton formed by the bond of silicon (Si) and oxygen (O), and which includes at least hydrogen as a substituent, or at least one selected from the group consisting of fluoride, alkyl group, and aromatic hydrocarbon as the substituent is referred to as siloxane based resin. The siloxane based resin is a kind of a heat resistant planarized film or a heat resistant interlayer (HRIL) film. Hereinafter, the term “heat resistant planarized film”, “heat resistant interlayer film”, “heat resistant resin”, or “HRIL” includes the siloxane based resin.
As droplet discharging for forming the conductive material or the insulating film, not only ink jetting but also offset printing or screen-printing can be used depending on the property of a film to be formed.
Conventionally, a source region and a drain region were formed by etching off a single conductivity semiconductor film after forming the island-like semiconductor film. Accordingly, it was necessary to provide a resist mask when forming an island-like semiconductor film. On the contrary, according to the present invention, after that a source region and a drain region are formed, an insulating film serving as a channel protective film is formed to cover a portion for serving as a channel region, then, an island-like semiconductor film is formed. Accordingly, a resist mask is not required to be provided, and so the process can be simplified. As discussed above, the present invention provides a novel means for forming a semiconductor element by combining a method for removing a single conductivity semiconductor film using a metallic mask of a source electrode and a drain electrode to form a source region and a drain region, and a method, which is specific to a channel protective type, for forming a channel protective film to prevent a channel region from removing. According to the foregoing configuration of present invention, a semiconductor element can be manufactured by using only a metallic mask of a source electrode and a drain electrode without using any resist mask.
Before discharging a composite containing a first conductive material over a substrate, a pretreatment such as the formation of a titanium oxide (TiOx) or the like may be conducted at least over the portion provided with a gate electrode layer over the substrate. Accordingly, the adhesiveness between the substrate and a conductive film such as the gate electrode layer formed by droplet discharging can be improved.
The gate electrode layer of the drive TFT can be connected to the drain electrode of the switching TFT without forming a contact hole by forming a pillar over the gate electrode layer of the drive TFT in connecting the gate electrode layer of the drive TFT to the drain electrode of the switching TFT.
The gate electrode layer of the drive TFT can be connected to the drain electrode of the switching TFT in accordance with the procedure, that is, a contact hole is formed by using a wiring formed by droplet discharging as a mask in connecting the gate electrode layer of the drive TFT to the drain electrode of the switching TFT; and the contact hole is filled with conductor.
By forming a semiconductor film provided with the insulating film to have a thinner thickness than that of another semiconductor film, an n-type impurity region can be divided into a source region and a drain region completely. By forming the semiconductor film provided with the insulating film to have a thickness of 10 nm or more, enough large channel mobility can be obtained.
By forming the insulating film to have a thickness of 100 nm or more, the function as a channel protective film can be improved and the channel region can be surely prevented from damaging. Accordingly, a stable semiconductor element having high mobility can be provided. Further, to obtain the foregoing advantage, it is effective that the insulating film is formed to have a two-layer structure composed of a first insulating film and a second insulating film, or three or more layered structure.